This paper summarizes an experimental study of three popular “turbulator” inserts for fire tube boilers. An electrically heated flow facility was developed to deliver hot air to a water-cooled steel tube instrumented to derive sectional average heat transfer coefficients for four regions of the tube. Reference data for the empty tube are in excellent agreement with the accepted correlation. Two commercial turbulators, consisting of narrow, thin metal strips bent and twisted in zig-zag fashion to allow periodic contact with the tube wall, displayed 135 and 175 percent increases in heat transfer coefficient at a Reynolds number of 10,000. A third commercial turbulator, consisting of a twisted strip with width slightly less than tube diameter, provided a 65 percent increase in heat transfer coefficient. The friction factor increases accompanying these heat transfer coefficient increases were 1110, 1000, and 160 percent, respectively, for the same Reynolds number. These data should be useful in assessing overall performance gains to be expected when turbulators are used in actual boilers.

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